Method for determining the amount of an operating medium in a motor vehicle

ABSTRACT

The invention relates to a method for determining the fill quantity of an operating medium, in particular of the engine oil in a motor vehicle having a reservoir container of the operating medium and having a data processing device for determining the fill quantity of the operating medium. A fill level sensor for sensing the fill level is arranged in the reservoir container for the operating medium. In order to determine the fill level of the operating medium, operating states of the vehicle such as the temperature of the operating medium and the engine speed are also sensed. According to the invention, a characteristic variable for the engine load, for example the position of the accelerator pedal, the throttle valve position or the torque on the drive train are sensed. The fill quantity of the operating medium is determined from the sensed data by a data processing device.

[0001] The invention relates to a method for determining the fillquantity of an operating medium in a motor vehicle, in particular thequantity of engine oil, according to the preamble of patent claim 1.

[0002] The genus-forming DE 19602599 A1 discloses a method fordetermining a quantity of fluid, in particular the quantity of engineoil, in a motor vehicle. The fill level of the fluid which is sensed bymeans of the fill level sensor fluctuates as a function of the drivingstate, as a result of which the determination of the quantity of fluidis adversely affected. In order to reduce the influence of thefluctuations in the fill level, which occur in particular in the drivingmode, variables which are indicative of the driving state are sensed andthe instantaneous driving state is determined from the variables whichare indicative of the driving state. During selected driving states, thefill level of the fluid is sensed and is used to determine the fillquantity of the fluid. This determination is carried out by reference toa known dependence of the fill level of the fluid on the fill quantityof the fluid and on the driving state. A precondition for the start ofthe method for determining the quantity of fluid is that fixedconditions for the temperature of the fluid, the ignition status of thespeed are fulfilled. The sensed fill level value is filtered digitally,as a result of which brief fluctuations in the fill level areeliminated. Furthermore, when the quantity of engine oil is determined,the engine speed is taken into account. It is to be noted that furthervariables, such as the speed of the vehicle, the temperature and thekilometer reading can be taken into account in the determination of thequantity of engine oil, and that statistical averaging of the measuredvalues further increases the reliability of the determination of aquantity of fluid.

[0003] If the vehicle is inclined, for example owing to uphill travel,the fluid reservoir container is inclined to the same degree and a fluidlevel which frequently differs from the fluid level of a horizontalvehicle depending on the location where the fill level sensor isinstalled, is obtained on the fill level sensor. If the quantity offluid is determined from the measured fluid level without taking intoaccount the angular position of the vehicle, an incorrect result may beobtained.

[0004] DE 4042472 C2 discloses an arrangement for determining thequantity of engine oil by measuring the engine oil level and measuringthe angular position of the vehicle. For each predefined quantity ofengine oil there is a uniquely defined relationship between the angularposition of the vehicle and the oil level in the engine. Thisrelationship is utilized in order to inferred the quantity of engine oilfrom the angular position of the vehicle and the oil level value. Theangular position of the vehicle is sensed using an angle measuringdevice, and the quantity of engine oil is calculated by means of a dataprocessing device using the angular position of the vehicle. The actualangular position and/or measured angular position of the vehicle relateto the gravity field of the earth. The two variables, the inclination ofa vehicle and the gradient (longitudinal inclination) of a road, alsorelate to this, moreover.

[0005] In another method for determining the fill quantity of theoperating medium, the fill level of the operating medium is sensed attwo or more locations in the reservoir container of the operatingmedium. Even when the angular position of the vehicle is unknown, thefill quantity can be calculated from the sensed fill levels, since thefill levels for each angular position are in a fixed relationship to oneanother which depends on the location where the fill level sensors aremounted and on the geometry of the reservoir container. However, inorder to carry out this method at least two fill level sensors arenecessary. Using two fill level sensors it is possible to determine theangular position of the vehicle in the direction of the line connectingthe two sensors. Furthermore, using three or more fill level sensorswhich are not arranged in a row it is possible to determine the angularposition of the vehicle in any desired direction, that is to say even inthe direction of the longitudinal axis of the vehicle and transverselywith respect to the longitudinal axis of the vehicle.

[0006] The object of the invention is to specify a method fordetermining the fill quantity of the operating medium which improvesthose known methods which have only one fill level sensor as a specificsensor. The object is achieved according to the invention by means ofthe features of claim 1.

[0007] The invention is based on a method in which the sensed fill levelof the operating medium is corrected by means of a plurality ofparameters which are used by a data processing device to determine thefill quantity of the operating medium. A fill level sensor is providedfor sensing the fill level in the reservoir container of the operatingmedium. Operating states of the vehicle are sensed as further parametersand made available to the data processing system. Examples of theseoperating states are the temperature of the operating medium and theengine speed.

[0008] In order to correct the influence on the sensed engine oil levelof the instantaneous gradient of the road being traveled on, a parameteris sensed which constitutes a measure of the gradient (longitudinalinclination) of the road. Such a parameter is the engine load whichbecomes larger when traveling uphill as the gradient increases and dropswhen traveling downhill as the gradient increases. According to theinvention, the gradient of the road is inferred from a characteristicvariable for the engine load, and the engine oil level is corrected bymeans of the gradient of the road. In order to supplement the engineload parameter, vehicle-movement-dynamic variables may be used whichgive an indication of the gradient of the road traveled on. An advantageof the method according to the invention is that the fill quantity ofthe operating medium is determined more precisely and reliably withoutadditional expenditure on sensors.

[0009] In one refinement of the method, the position of the acceleratorpedal is sensed as the characteristic variable for the engine load andis used to determine the fill quantity of the operating medium. Theposition of the accelerator pedal is a variable which acts directly onthe power generation of the engine and is thus characteristic of theload of the engine. In addition, the position of the accelerator pedalis a variable which is already available as a signal on a data bus.

[0010] In another refinement of the method, the throttle valve positionis used as the characteristic variable for the engine load. In manyvehicles, this variable is also available on a data bus in the vehicle.

[0011] In an alternative refinement of the method, a physical variablesuch as force, torque or power on the drive train, that is to saybetween the engine and the wheel, is sensed as the characteristicvariable for the engine load. Such a variable is a direct measure of theengine load.

[0012] The method according to the invention can be applied inparticular for determining the fill quantity of fluids in reservoircontainers in the vehicle, for example gear oil, brake fluid, coolant orfuel.

[0013] There are then various possible ways of advantageouslyconfiguring the teaching of the present invention. One advantageousembodiment of the method according to the invention for determining thefill quantity of the operating medium in a vehicle will now be explainedin more detail below with reference to the drawing.

[0014]FIG. 1 shows a flowchart of an advantageous embodiment of themethod in a schematic illistration. The fill level is related to thefill quantity in a uniquely defined way, as a result of which the fillquantity can be determined from the fill level, for example by means ofa functional relationship using a characteristic curve or a table. Animproved determination of the fill quantity of an operating medium canthus be achieved by means of an improved determination of the fill levelof the operating medium. Here, the determined fill level is to beunderstood as a value which corresponds to a fill level which ismeasured under predetermined conditions, and may vary from the actuallymeasured fill level. A corrected fill level Xcorr is determined from afill level X by means of the illustrated embodiement of the method, saidfill level Xkorr corresponding better to the actual fill quantity thanthe fill level X.

[0015] The method according to the invention is started as a function ofpredefinable starting conditions. These starting conditions relate, forexample, to the temperature of the operating medium, the speed of thevehicle, the engine speed, the ignition status, the status of electricalloads, the transverse acceleration, the longitudinal acceleration andthe yaw rate. These parameters may not only be included in the startingconditions but also in abort conditions for the method according to theinvention.

[0016] In addition to the starting and abort conditions, conditions forthe sensing of measured values may also be predefined. If theseconditions are not fulfilled, no measured values are sensed or thesensed measured values are not used to determine the fill quantity ofthe operating medium. The same parameters can be included in theconditions for the sensing of measured values as in the startingconditions.

[0017] The flowchart is selected for the case of uphill travel, and thefill level sensor is arranged in such a way that during uphill travel,that is to say when the vehicle is inclined to the rear, the fill levelof the operating medium at the fill levels sensor is lower.

[0018] In method step 101, the fill level X is read in. The fill level Xis a value which is obtained from processing the value which is sensedby the fill level sensor. For example, the fill level X can be obtainedfrom the sensed fill level by filtering using a low-pass filter, or thevalue X may be a chronologically averaged value of the fill level sensedby the fill level sensor.

[0019] In the interrogation 102 it is checked whether the fill level Xis lower than a predefined value Xef. If this is the case, in step 103it is checked whether the load signal L (a characteristic variable forthe engine load) which is read out from a data bus of the vehicle instep 104, is larger than a predefinable value LBerg. This value LBergdepends in particular on the geometry of the operating medium reservoircontainer and on the location where the fill level sensor is mounted.Given a geometry of the operating medium reservoir container with astrong change in the fill level at the fill level sensor even on smallgradients, the value Lberg is selected to be smaller, whereas given ageometry of the operating medium reservoir container in which thegradient of the uphill travel has only a small influence at the filllevel on the fill level sensor, a relatively large value for LBerg ispredefined. If the load signal L is greater than the predefined valueLBerg, in step 105 it is checked, over a predefinable time period,whether the conditions 102 and 103 are fulfilled, that is to say whetherthe fill level X is lower than a predefined fill level Xdef, and thecharacteristic signal for the engine load L is larger than a predefinedthreshold value LBerg. If the two conditions 102 and 103 are fulfilledfor a time period tdef or longer, in step 106 the fill level X iscorrected by adding a value x to the fill level X.

[0020] A gradient of the road and an acceleration process have the samephysical effect owing to the identity of inertial mass and gravitationalmass. However, while uphill travel can have relatively long gradientswhich change little, acceleration processes with a virtually constantacceleration of the vehicle rarely last longer than 10 or 20 seconds.The combined checking of the steps 103 and 105 thus corresponds toindirect checking to determine whether the gradient of the road isgreater than a predefined gradient because short acceleration processesare eliminated by the time interroation 105, if, for example, tdef=15 sis selected.

[0021] The correction of the fill level in step 106 can take the form ofa simple addition of a constant correction value. Alternatively, thecorrection term may also be a function of other parameters, for examplethe gradient, the load, the operating medium temperature or the vehicleload.

[0022] If one of the conditions 102, 103 and 105 was not fulfilled, thatis to say if the fill level X is larger than a predefined value Xdef, ifthe load signal L is smaller than the predefined value LBerg or if thetwo conditions are not fulfilled for at least one predefined time periodtdef, the system branches to step 107 starting from the respectiveinterrogation, and the fill level X is left unchanged, that is to saythe corrected fill level Xkorr is equal to the fill level X. The filllevel Xkorr, or the fill quantity which is determined from Xkorr, isindicated in step 108. Alternatively, or in addition, the corrected filllevel Xkorr or the fill quantity calculated therefrom can be madeavailable for further processing.

[0023] In a more complex embodiment of the method, a plurality ofthresholds are predefined for the fill level X, the load L and the timet, and different correction terms x are added to the fill level X as afunction of the exceeded thresholds. A functional relationship betweenthe parameters X, L, t and x can also be predefined in order to correctthe fill level X.

[0024] The method for determining the fill quantity of the operatingmedium which is illustrated in FIG. 1 is changed, in the event of uphilltravel in step 103, to the effect that the sign of the interrogation isreversed and a different value is predefined for LBerg. In addition,given the same arrangement of the fill level sensor, that is to say atthe rear of the filling trough, the sign in step 102 is reversed and adifferent value Xdef can be predefined.

[0025] If the fill level sensor is arranged at the front of thereservoir container of the operating medium, the sign is reversed instep 102 in comparison with the same cases with an arrangement of thefill level sensor in the rear region of the reservoir container.

1. A method for determining the fill quantity of an operating medium, inparticular the quantity of engine oil, in a motor vehicle having areservoir container for the operating medium, having a fill level sensorfor sensing the fill level in the reservoir container, and having a dataprocessing device for determining the fill quantity of the operatingmedium, in which the fill level of the operating medium and operatingstates of the vehicle are sensed, and in which the fill quantity of theoperating medium is determined from the sensed data by the dataprocessing device, characterized in that a characteristic variable forthe engine load is sensed and is used to determine the fill quantity ofthe operating medium.
 2. The method for determining the fill quantity ofan operating medium in a motor vehicle as claimed in claim 1,characterized in that the position of the accelerator pedal is sensed asthe characteristic variable for the engine load and is used to determinethe fill quantity of the operating medium.
 3. The method for determiningthe fill quantity of an operating medium in a motor vehicle as claimedin claim 1, characterized in that the throttle valve position is sensedas the characteristic variable for the engine load and is used todetermine the fill quantity of the operating medium.
 4. The method fordetermining the fill quantity of an operating medium in a motor vehicleas claimed in claim 1, characterized in that a force on the drive trainis sensed as the characteristic variable for the engine load and is usedto determine the fill quantity of the operating medium.
 5. The methodfor determining the fill quantity of an operating medium in a motorvehicle as claimed in claim 1, characterized in that a torque on thedrive train is sensed as the characteristic variable for the engine loadand is used to determine the fill quantity of the operating medium. 6.The method for determining the fill quantity of an operating medium in amotor vehicle as claimed in claim 1, characterized in that a power levelon the drive train is sensed as the characteristic variable for theengine load and is used to determine the fill quantity of the operatingmedium.